Project Summary- Development of effective treatments for patients with amyotrophic lateral sclerosis (ALS) is currently hindered by the lack of validated therapeutic targets. Our long-term goal is to use motor neuron-based cell and animal models to better understand the molecular and cellular mechanisms involved in ALS, and to validate these as targets for clinical intervention. Motor neurons purified from SOD1 mutant mice, a model of familial ALS, show selectively exacerbated sensitivity to activation of a new cell death pathway involving the Fas death receptor and nitric oxide (referred to as the Fas/NO pathway). All elements of the pathway are activated in the spinal cord of presymptomatic SOD1 mice. The project will address four questions: (a) Is the Fas/NO pathway an essential contributor to the disease process in vivo in SOD1 mutant mice? (b) Which cell types are involved in activation of the Fas/NO pathway in vivo? (c) How does mutant SOD1 sensitize motor neurons to activation of the Fas/NO pathway? (d) What is the relevance of the Fas/NO pathway to sporadic ALS in humans? We will cross conditional knockout mice for Fas and FasL to SOD1 mutant mice and measure effects on motor function, survival and pathology. We will analyze the sites of Fas action in vivo using a biomarker approach. Lastly, we will analyze expression of elements of the Fas/NO pathway on sections of spinal cord from human patients with sporadic ALS. Overall, the work will provide new insights into mechanisms of motor neuron degeneration in vitro and in vivo and should allow for validation of new therapeutic targets in both familial and sporadic ALS. Relevance Amyotrophic lateral sclerosis (ALS), better known as Lou Gehrig's disease, leads rapidly to paralysis and death of patients, reflecting progressive loss of motor neurons, the nerve cells in the spinal cord that control muscle movement. This study will use cell and animal models to better understand the molecular events that underlie ALS as a means for developing rational therapeutic strategies.